Darth Revan & ROTS Vader vs. ROTS Yoda & ROTS Grievous

'Revan should be the strongest one with Yoda, because he was a lightsaber prodigy. I wouldn't put Vader, nor Grievous in a league with Revan, especially while Vader's a robot and GG was pwned by Obiwan..'

Anakin would also be a prodigy.

Anakin was an unparalleled Force and saber prodigy. Luke is too.

The exact circumstances of Revan's prodigious skills have yet to be released.

Revan could take them both without vader